1. Field of the Invention
The present invention generally relates to a load controlling apparatus for controlling a desired quantity of power supplied from a common power source to a plurality of electric loads. More specifically, the present invention is directed to a load controlling apparatus capable of preventing occurrences of failure of other relevant circuits, and capable of quickly judging work contents of maintenance or repair.
2. Description of the Related Art
In general, when desired power is supplied from one power supply source to a plurality of loads in response to a control signal supplied from a central processing unit, both a power supplying time period and an amount of power per unit time to the load via a drive circuit are controlled. In the conventional load controlling apparatus including such a drive apparatus, a microprocessor (simply referred to as a "CPU" hereinafter), and a semiconductor drive device have readily been employed because of the technical progress in the semiconductor devices. Since a plurality of load devices having various variations are combined and controlled in such a conventional load control apparatus, a predetermined long time is required from occurrences of disconnections and shortcircuits in the load till repairing work, so that the load controlling apparatus including the protection circuit and diagnostic circuit has been required. As one example of the above-described load drive apparatus, a conventional load controlling circuit for an automobile will now be described with reference to FIGS. 8 to 10.
FIG. 8 is a circuit arrangement of a conventional load controlling apparatus including a protection circuit where in response to a voltage signal appearing across the load, a signal input from a control circuit is interrupted at a drive circuit. FIG. 9 is a circuit arrangement of a conventional load controlling circuit including a protection circuit for interrupting an output signal derived from the control circuit based upon a value of a current flowing through the load. FIG. 10 is a circuit arrangement of a conventional load controlling apparatus including a protection circuit for interrupting the output of the control circuit based on both the load voltage and the load current, and also a diagnostic circuit for displaying the result of this diagnostic operation.
In figures, reference numeral 1 is a load; reference numeral 2 denotes a current detecting circuit of the load; reference numerals 3, 301, 302 represent drive circuits; reference numerals 401, 402 indicate control circuits; reference numeral 501 denotes a diagnostic circuit; a symbol D18 indicates a diode; a symbol Q11 is an NPN type bipolar transistor; a symbol Q12 represents a PNP type bipolar transistor; a symbol RS denotes a resistor for detecting a current value; a symbol Q13 indicates a power drive type N-MOS field effect transistor having a current detecting terminal; and a symbol "V" indicates a positive polarity power source terminal.
At first, the conventional load controlling apparatus having the protection circuit of the drive element caused by the load voltage will now be described with reference to the circuit arrangement shown in FIG. 8.
A circuit construction will be first of all described. The control circuit 401 converts an operation signal "f" produced upon the selecting operation or the like, which is input via a CPU (not shown), into a control signal "a" for supplying power to a load (lamp, motor, solenoid, heater etc.) and then supplies this control signal "a" to the drive circuit 301.
To an input unit into which the control signal "a" of the drive circuit 301 is supplied, both the base of the load driving transistor Q11 and the anode of the protection circuit diode D18 for this transistor Q11 are commonly connected. One terminal of the load 1 is connected to the emitter of the transistor Q11, whereas the power supply terminal V is connected to the collector thereof. It is so arranged that the load current flows through the other end of the load 1 connected to the load drive device by the common ground line, and the negative polarity power source terminal (not shown) connected to this common ground line, from the power source.
The base of the transistor Q12 for the protection circuit is connected to a junction between the load 1 and the emitter of the transistor Q11 so as to detect the voltage applied to the load 1, and the emitter of which transistor Q12 is connected to the cathode of the diode D18. The transistor Q12, to the base of which the voltage detection signal "C" has been supplied at a level lower than a predetermined value, will draw the base voltage of the transistor Q11 via the diode D18 to the ground potential side, since the collector of the transistor Q11 is connected to the ground line.
Then, an operation of the circuit arrangement shown in FIG. 8 will now be described. When, for instance, both ends of the load 1 are shortcircuited, the base potential of the transistor Q12 is drawn adjacent to the ground level. A portion of the supplied control signal "a" is flown through the diode D18 into the emitter-to-base of the transistor Q12. Consequently, a great control signal "a" is also flown through the emitter-to-collector of the transistor Q12. Then, since the base voltage of the transistor Q11 cannot reach the voltage level at which the predetermined power can be supplied to the load 1, the overcurrent destruction of the transistor Q11 due to the load circuit or the like can be protected.
Then, the conventional load drive apparatus including the protection circuit of the drive element by the detection signal of the load current will now be explained with reference to the circuit arrangement of FIG. 9. It should be noted that the same or similar reference numerals shown in FIG. 8 will be employed as those for denoting the same or similar circuit portions and functioning portions in the following figure, and therefore, detailed descriptions thereof will be omitted.
First, the circuit arrangement will be described. The control circuit "a" output from the control circuit 402 in accordance with the operation signal "f" is supplied to the drive circuit 3. The voltage is so applied from the power source terminal V that the load current is flown through the current detecting circuit 2 interposed between the drive circuit 3 and load 1, for detecting the load current value, the other end of the load 1 and the negative polarity terminal of the power source via the ground line.
The current detecting circuit 2 outputs a current detecting signal "b" in accordance to an internal impedance variation of the drive circuit 3 and a load impedance variation based upon the control signal "a" to the control circuit 402 with a variation in the voltage value.
The control circuit 402 adjusts the control signal "a" and supplies it to the drive circuit 3 under the condition that when the feedback current detecting signal "b" is equal to a predetermined value, the load current lower than the rated current value of the load 1 is flown during only the time in accordance with the operation signal "f".
Operations of the circuit arrangement shown in FIG. 9 will now be described. When the impedance of the load 1 is lowered in case that, for instance, a mechanical load for a motor or the like is extraordinarily increased, such a high current value which will exceed over the rated current value of the load 1 or the drive element of the drive circuit 3 is detected by the current detecting circuit 2. This high current may electrically destroy the load 1 or drive element. In the control circuit 4 into which the current detecting signal "b" has been supplied in response to this current detection, the internal impedance of the drive circuit 3 is increased and therefore the negative feedback operation is carried out only during the time period determined by the operation signal "f" of all of the input conditions, by which the load current is lower than the rated current value of the load 1 or drive element.
However, since in the load drive apparatus including the above-described protection circuit for the drive element, it cannot immediately detect how the load 1 is brought into the malfunction, the following diagnostic apparatus is required so as to diagnose the circuit portion to be repaired.
Referring now to the circuit diagram of FIG. 10, the conventional load drive apparatus including the diagnostic circuit for diagnosing the load malfunction conditions based upon a detection signal for both such a load current and a load voltage, and also the protection circuit of the drive element. It should be noted that the same or relevant reference numerals shown in FIGS. 8 and 9 will be employed for denoting the same or similar circuit portions shown in FIG. 10, and a detailed description thereof will be omitted, accordingly.
A circuit arrangement of FIG. 10 will be first described. The control signal "a" is supplied to a gate of a transistor Q13 arranged in a drive circuit 302. A drain D of this transistor Q13 is connected to the power source terminal "V", a source S thereof is connected via the load 1 to the ground line, and a terminal "K" for detecting a current is connected via a resistor "RS" to a junction between the load 1 and source S. From the junction between the terminal K and resistor RS, a voltage value corresponding to a current value flowing through the drain D to source S of the transistor Q13 is supplied as the current detection signal "b" to the diagnostic circuit 501. Also from the junction among the load 1, resistor RS and transistor Q13, a voltage is applied as the voltage detection signal "C" applied to both ends of the load 1 to the diagnostic circuit 501.
The diagnostic circuit 501 will diagnose that the circuit of the load 1 is interrupted, or disconnected under the conditions that the current detection signal "b" input to this diagnostic circuit 501 is equal to a value indicating that no current flows into the load 1, and also the voltage detection signal "C" is substantially equal to a value representing the voltage value of the power source terminal V. In addition, this diagnostic circuit 501 will diagnose that the load 1 is short-circuited under the conditions that the current detection signal "b" is equal to a value indicating that the load current exceeds over the allowable rated current value of the load 1, and also the voltage detection signal "c" is equal to a value representing that it is lower than a predetermined voltage. Then, this diagnostic apparatus will diagnose that the circuit is normally operated under other conditions. From this diagnostic circuit 501, a feedback signal "e" is supplied to the control circuit 402 by which based upon the shortcircuit diagnostic condition of the load 1, the internal impedance of the drive circuit 302 is maximized, and a display signal "d" is output via a CPU (not shown) to a display device by which the shortcircuit condition is displayed, and furthermore, the display signal "d" is output to the display device, for displaying that the circuit of the load is interrupted or disconnected.
Operations of the load controlling apparatus shown in FIG. 10 will now be described. When, for instance, the circuit of the load 1 is disconnected, as the voltage induced at the current detecting terminal k of the transistor Q13 is substantially equal to the voltage of the source S of the transistor Q13, no current is flown into the resistor RS for detecting the current, which is connected between the terminal K and source S. Accordingly, both the current detecting signal b and voltage detecting signal c having the equal "H" levels are output. Then, from the diagnostic circuit 50 to which two "H"-leveled signals have been continuously supplied during more than a predetermined time period, only the display signal d is output to the CPU with having the "H" level for displaying that the circuit of the load is disconnected. Under this condition, this CPU performs the display operation of the malfunction condition under of the load 1 which the internal impedance of the load 1 becomes extraordinarily high, i.e., open circuit condition.
To the contrary, when the load 1 is brought into the shortcircuit condition, the voltage induced at the current detecting terminal "K" of the transistor Q13 to which the "H"-leveled control signal "a" is applied, exceeds over the voltage of the drain "D" to which the load 1 is connected. As a result, the current detecting signal "b" which is higher than the "L"-leveled voltage detecting signal "C" is output to the diagnostic circuit 501. Then, from the diagnostic circuit 501 to which these two signals having the above-described conditions have been continuously supplied over a predetermined time period, the L-leveled display signal "a" representative of the shortcircuited load 1 is output to CPU. At the same time, from the diagnostic circuit 501, the feedback signal "e" is output to the control circuit 402. This feedback signal "e" is to change the internal impedance between the source "S" and drain "D" of the transistor Q1 employed in the drive circuit 302 into its the maximum value. Under this condition, CPU outputs the display signal "a" for displaying that the load is brought into the shortcircuit condition. Since the over-current does not flow through the transistor Q13 due to the "L"-leveled control signal "a" supplied to the gate "G" thereof, the destruction of this transistor Q13 is prevented.
However, according to the above-described prior art load controlling apparatus including the diagnostic circuit, since based upon the voltage value applied to the load 1 and the current value flowing through the load 1, the extraordinary condition is diagnosed to protect the drive element, the diagnostic result is given in such a way that the malfunction occurs in the load 1 even if the drive element itself is brought into the extraordinary condition such as open-circuit failure. As a consequence, a long time is required to repair the failed load controlling apparatus, and the proper protection as well as proper recovery operation cannot be performed.
As a result, an object of the present invention is to provide a load controlling apparatus by which the correct diagnostic display for the failed portion can be performed, and the repairing work can be quickly effected, and thus, the proper circuit protection operation can be executed.